Process for extracting precious metals



Nov. 15, 1938. L. BICE ET AL 2,136,409

PROCESS FOR EXTRACTING PRECIOUS METALS Filed Sept. 28, 1936 Zincentors Zorirv Bice Q'l'z Fred Scalar attorneys.

Patented Nov. 15, 1938 UNITED STATES PATENT- OFFICE PROCESS FOR EXTRACTING PRECIOUS METALS Application September 28, 1936, Serial No. 103,018

2 Claims.

The present invention relates to improvements in the process for the extraction of precious metals from ores containing values of the same.

An object of the invention is to dissolve the metals in a short period with a single extracting operation.

A further object is to provide an improved mixture of reagents which softens the ore quickly and dissolves out the precious metals.

Another object is to provide a process in which copper dissolved out of the ore is removed from the extracting solution from time to time to preserve the purity of the same.

A further object consists in providing a process in which theore and solution are so agitated as to improve greatly the solvent action of the reagents.

When the invention is used with sulphide ores the process contemplated is adapted to ores with a copper content of less than three percent. The ores may or may not have coarse gold.

With the foregoing and other objects in view, the invention will be more fully described hereinafter, and will be more particularly pointed out in the claims appended hereto.

The drawing is a side elevation of the apparatus employed partly in section.

The device consists generally in a high pressure drum l0 of steel or the like provided at opposite ends with trunnions ll secured by any suitable means to the end of the drum. A pair of supports I2 is provided spaced apart sumciently to receive the drum therebetween and each provided at its upper portion with a bearing l3 which may be of the split block type and provided with an adjustment screw It. The ends of the trunnions II are projected through the respective bearings l3. One of .the trunnions l l is longer than the other so as to extend a substantial distance beyond the bearing l3 to receive a belt pulley l5 which is adapted to hold a belt driven in any suitable manner to rotate the drum.

The drum I 0 is provided at one point on its surface with a large opening IS in which is placed the closure H. The size of the opening I6 is such that ore may be shoveled into the drum through it. The closure I1 is screw-threaded into the opening l6 for a tight fit and is provided at its outer side beneath the head with a compressible ring l8 to completely seal the opening.

At another point in the drum is placed an air valve l9 which is threaded through an opening in the drum and which contains a check valve to hold the pressure within the drum.

At a third point in the drum is placed a water introducing valve 20 threaded into the wall of the drum and having at its outer end a threaded nipple 2! adapted to receive a threaded coupling from a hose or the like.

The ore is now prepared by grinding and a quantity is placed in the drum ID. A quantity of water is introduced into the drum through the valve 20. The reagents may now be added to the contents of the drum or they may have been mixed with the water prior to the introduction of the latter into the drum. The. reagents comprise a cyanide salt such as sodium cyanide and an ore softening substance. This ore softening has been discovered to be accomplished best by a small quantity of sodium chloride in the reagent mixture. If there is coarse gold in the ore it will be necessary to add a small quantity of aqua regia. When the reagents are added the valve 20 is closed and air under pressure is introduced through the valve IS. The pressure of the air depends on the characteristics of the particular ore and will vary from fifty to five hundred pounds per square inch. When the air under suitable pressure has been introduced the drum is rotated for a period sufiicient to complete the penetration of the reagents into the ore to dissolve all of the precious metals.

As the ores may contain copper, which will be dissolved by the reagents, it is desirable to remove the solution or portions thereof from time to time and purify it of copper. This may readily be accomplished by drawing the solution into a container with scrap iron or some other more electropositive metal which will cause the precipitation of the copper. The purified solution may then be returned to the drum and continued in use.

By way of specific example it has been found that with an ore containing some coarse gold the following proportions and conditions were best:

One ton of the ground ore was placed in the drum Ill. The reagent solution was made up of one hundred and fifty gallons of water, two pounds of sodium cyanide, one ounce of sodium chloride and one sixteenth ounce of aqua regia. This solution was introduced through the valve 20 into the drum l0 and after its introduction air at a pressure of about one-hundred pounds per square inch was introduced through the valve IS. The drum was now rotated at the rate of ten revolutions per minute for a period of one hour. At the end of this time all of the gold and silver of the ore was dissolved in the reagent solution. The solution was then withdrawn and the metals the reagent solution into the ore and the proper pressure for each ore will depend upon the nature of the particles to be penetrated. For example, porphyry ores require lower pressure than others, but white sulphide quartz requires more pressure, while the average sulphide ore responds to one hundred pounds of pressure to-the square inch.

It will readily be seen that there are very few operations to be conducted in this extracting process and the rate of dissolving the metals is much more rapid than by the usual means employed.

The process eliminates the use of mercury or amalgams and also the use of the electro-depositing methods previously employed in the art.

The elimination of the mercury treatment is a great saving in expense and time in the treatment. The process is a cold process requiring no heat and being conducted entirely in solution and this eliminates -the necessity for costly apparatus and the maintenance of expensive high temperature reactions.

Another important advantage gained by the process is that fine grinding of ores is unnecessary. The process operates successfully on ores ground to thirty mesh. This is a great saving in operating and machine costs. The thirty mesh grinding leaves a fairly coarse ore which would be difiicult of extraction by previously known processes but which is perfectly satisfactory when extracted by the present process.

It is obvious that various changes and modifications may be made in the details of construction and design of the above specifically described embodiment of this invention without departing from the spirit thereof, such changes and modifications being restricted only by the scope of the following claims.

What is claimed is:

1. The process of extracting precious metals from ores by cyanidation, comprising grinding the ore to a coarse mesh, mixing therewith a solution of an alkali cyanide, agitating said mixture under pressure in a rotating drum and in the presence of aqua regia, and thereafter recovering the precious metal from the solution.

2. The process of extracting precious metals from ores by cyanidation, comprising grinding the ore to a coarse mesh, mixing therewith a solution of an alkali cyanide and a small amount of sodium chloride, agitating said mixture under pressure in a rotating drum and in the presence of aqua regia, and thereafter recovering the precious metal from the solution.

LORIN BICE. FRED SOULAR. 

